As shown in the figure, in raising the arm, there are three forces that have to be considered;
the force exerted by the shoulder Fs and it acts on the humerus along the +ve x-axis. Second the
weight, Fa, of the arm and the third force is that of the deltoid muscle, Fd, which acts at
approximately 15o as shown in the figure. If Fa is 15 N, what are the magnitudes of Fs and Fd
when the arm is held fixed at the position shown?
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